Each kind of food has a different level of digestibility which results from both the way it is processed and the ingredients used. The least digestible in terms of processing is dry extruded, or kibble, and the most digestible forms are frozen and raw diets. The range of digestibility in pet food ingredients also varies considerably. This should be taken into account when choosing a food because it is not enough for a nutrient to be found in a food if that food is not high ly digestible. Ingredients in many popular foods that rank low in terms of digestibility are corn, soy, wheat and meals. Dogs must consume larger amounts of these foods in order to meat the same nutritional levels of foods that contain highly digestible ingredients such as whole meats, whole grains, and whole vegetables. This is one reason why dogs may gain weight when being fed a food that is difficult to digest.